The invention relates to a process for cleaning a surface of a semiconductor wafer following a chemical mechanical polishing step and to a device for carrying out a process of this type.
Chemical mechanical polishing (CMP) is increasingly being used in the fabrication of semiconductor components, in particular belonging to the sub-0.5 xcexcm generation, to planarize the topology which is produced on the semiconductor wafer during the fabrication processes. The chemical mechanical polishing is used predominantly to level trench fillings, metal plugs, e.g. plugs of tungsten in contact holes and vias, and intermediate oxides and intermetal dielectrics.
For chemical mechanical polishing, the semiconductor wafer which is to be polished is pressed by a wafer support onto a rotatable polishing table on which there is an elastically perforated pad which contains a polishing slurry. The semiconductor wafer and the polishing table rotate in opposite directions, with the result that the surface of the semiconductor wafer is polished down at the protruding locations until a substantially completely planar wafer surface is reached. In addition to abrasive polishing grains, the polishing slurries generally contain further active chemical additives which allow selective removal of the layers on the semiconductor wafer. In this context, a distinction is drawn between what is known as a blind polishing process, i.e. a polishing process which is stopped within the layer which is to be polished, and what is known as a stop layer polishing process, wherein the polishing operation is selective with respect to a further layer lying below the layer which is being polished.
During the chemical mechanical polishing operation, slurry impurities are generally left behind on the surface of the semiconductor wafer. The remaining slurry impurities have to be removed in a subsequent cleaning process. For this cleaning operation, after the polishing operation first of all the semiconductor wafers are stored in a water bath, and then the surface impurities are removed using what is known as a brush cleaner. During the brush cleaning, the semiconductor wafer is rinsed continuously with distilled water and/or ammonia. After the brush cleaning process, the semiconductor wafer is then dried by rapid rotation in a drying station. The brush cleaning process illustrated is a single-wafer process, and consequently the wafer throughput is greatly restricted. Furthermore, the required loading and unloading of the brush cleaner and of the drying centrifuges additionally makes the cleaning process very time-consuming. Furthermore, there is a high consumption of distilled water or ammonia during the brush cleaning process.
Instead of the wafer surface being cleaned with the aid of a brush cleaner, a wet cleaning process using chemical baths is also used, wherein the semiconductor wafer is slaved through a plurality of successive cleaning baths, during which process in particular the chemically bonded slurry residues on the semiconductor surface are removed. This chemical cleaning is followed by rinsing with distilled water and then wafer drying; in this case it is preferable to use the so-called Marangoni drying process, wherein the semiconductor wafers are drawn through an isopropanol solution and are then dried in hot nitrogen. With the wet-chemical cleaning process shown, it is possible to clean a plurality of semiconductor wafers simultaneously, with the result that a high wafer throughput can be achieved. However, in this case too the high consumption of chemicals in the cleaning operation and the high outlay on equipment cause problems.
It is accordingly an object of the invention to provide a method and a device for cleaning a semiconductor wafer which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allows the removal of impurities which remain on a semiconductor wafer during chemical mechanical polishing quickly and effectively with little outlay on equipment.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor wafer processing method, which comprises:
subjecting a surface of the semiconductor wafer to a chemical mechanical polishing step; and
cleaning the wafer surface of the semiconductor wafer by performing the following steps while continuously rotating the semiconductor wafer:
etching the wafer surface;
rinsing the wafer surface; and
drying the wafer surface.
In accordance with an added feature of the invention, the chemical mechanical polishing step is used to planarize an oxide, and, in that case the following process steps are carried out, while continuously rotating the semiconductor wafer:
rinsing with ozonized distilled water;
etching with an HF solution;
rinsing with ozonized distilled water; and
drying with a gas mixture of isopropanol and nitrogen.
In accordance with an additional feature of the invention, the chemical mechanical polishing step is used to planarize a layer of metal on the semiconductor wafer. In that case, the following process steps are carried out, again while continuously rotating the semiconductor wafer:
etching with an HF solution or an H2SO4 solution with HF and H2O2 additions;
rinsing with ozonized distilled water; and
drying with a gas mixture of isopropanol and nitrogen.
In accordance with another feature of the invention, the speed with which the semiconductor wafer is rotated is increased for the drying step.
In accordance with a further feature of the invention, the semiconductor wafer is stored in a water bath between the chemical mechanical polishing step and the cleaning step.
In other words, to clean a surface of a semiconductor wafer following a chemical mechanical polishing step with the semiconductor wafer rotating continuously, the semiconductor wafer is, in succession, firstly rinsed with an etching liquid, then preferably rinsed again with distilled water and then preferably dried using an isopropanol-nitrogen mixture.
This integrated procedure in accordance with the invention makes it possible to combine the process steps, which have hitherto been carried out separately during cleaning, so that process time can be saved and, at the same time, the wafer throughput can be significantly increased. Furthermore, considerable amounts of etching chemicals and distilled water can be saved in particular as a result of the cleaning operation being carried out with the wafer rotating continuously.
According to a preferred refinement, the etching liquid used is of a HF solution, a buffered HF solution or a solution of H2SO4, H2O2 and HF. Etching solutions of this type can reliably be used to eliminate slurry impurities such as those which occur in particular in oxide or metal planarization with the aid of a chemical mechanical polishing operation.
With the above and other objects in view there is also provided, in accordance with the invention, a semiconductor wafer processing device, comprising:
a device formed with a process chamber for receiving a semiconductor wafer following a chemical mechanical polishing process and for cleaning a surface of the semiconductor wafer with the above-summarized method;
a loading and unloading station for placing the semiconductor wafer in the process chamber and a turntable for holding and rotating the semiconductor wafer; and
a feed for process media for cleaning the semiconductor wafer communicating with the process chamber, and a return for the process media for cleaning the semiconductor wafer communicating with the process chamber.
In accordance with again an added feature of the invention, the process chamber has independent process stations for the individual cleaning steps, and the turntable is displaceable between the process stations.
In other words, the cleaning device according to the invention has a process chamber which has a loading and unloading station for the semiconductor wafers, a turntable for holding and rotating the semiconductor wafer, and feeds and returns for the process media used to clean the semiconductor wafers. A configuration of this type means that only a single process chamber is required for the entire cleaning operation, including the drying, resulting in a significant saving on equipment. Furthermore, the semiconductor wafer remains in a single chamber throughout the entire cleaning and drying operation, with the result that in particular the risk of surface defects is significantly reduced.
In accordance with a concomitant feature of the invention, there is provided a wet handler connecting the loading and unloading station of the process chamber to a chemical mechanical polishing installation. That is, it is preferred for the process chamber for the cleaning and drying operation to be directly connected to the device for chemical mechanical polishing via a wet handler. This allows an integrated polishing and cleaning process, ensuring a minimal defect density on the semiconductor wafer.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a process and device for cleaning a semiconductor wafer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.